Py2.3: Feedback on Sets (fwd)

[David Mertz]

|mertz at gnosis.cx (David Mertz) wrote
|> Then again, power set really is a fundamental operation
|> on sets.  And making users rewrite it each time is error prone.

pwmiller1 at adelphia.net (Paul Miller) wrote previously:
|How is it error prone?  if P is the power set operation, and S and X
|are sets, then X in P(S) is equivalent to X is a subset of S.  I don't
|think that's all that error prone.

This looks more like a definition of a method Set.ispowerset(), not one
of Set.powerset().  The actual generation of P(S) is the part I think
programmers could do wrong.  I'm not saying that they might not usually
do it right... but mistakes happen.

Raymond Hettinger also wrote:
|from sets import Set
|def powerset(iterable):
|    data = list(iterable)
|    for i in xrange(2**len(data)):
|        yield Set([e for j,e in enumerate(data) if i&(1<<j)])

Hmmm...  I should have checked the docs first.  A sample implementation
obviously helps.  That said, this isn't REALLY an implementation of
powerset.  It returns an iterator, not a set.  Now, sure... an iterator
is a BETTER thing to get, for lots of reasons.  But I'm not sure it
lives up to the function name.

Yours, David...

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